Abstract
YbCu4Ag crystallizes in the cubic AuBe5-type structure where Yb is trivalent and shows dense Kondo behavior, while YbCu5 is known to have the hexagonal CaCu5-type structure where Yb is in a nonmagnetic divalent state. In this study, a pseudo-binary system YbCu5-xAgx was investigated. The powder Xray diffraction revealed that YbCu5-xAgx has the cubic AuBe5-type structure in the range of 0.125≤x≤1.0, while both the cubic and the hexagonal phase exist for 0≤x≤0.1, which suggests YbCu5 has also cubic AuBe5-type where Yb seems to be trivalent. Magnetic and transport properties show that YbCu5-xAgx is a dense Kondo system in which Kondo-temperature TK decreases continuously with the decrease of Ag-concentration x, causing the enhancement of the zerotemperature susceptibility x(O), the T2-coefficient A of electrical resistivity and the Sommerfeld coefficient γ of specific heat. The γ value was found to be enhanced to as large as 460mJ/mo1K2 in YbCu4.875Ag0.125. These results imply the cubic AuBe5-type YbCu5 is a dense-Kondo or a heavy-fermion system, in which γ reaches to about 500mJ/molK2.
